In semiconductor manufacturing, a plating tool uses a negatively charged anode (usually a copper anode) to plate a positively charged (cathode) silicon wafer. The anode provides a source of replenishing metal ions. At the cathode, the metal ions are reduced to metal and deposited on the cathode surface. Sulfuric acid and a plating solution flows through a chamber around the anode and is used to dissolve a metal (copper) plate. As fluid flows past the anode, it becomes enriched with metal ions.
During the chemical reaction that dissolves the metal (e.g., copper), hydrogen gas is liberated. In addition, entrapped gases are generally present during start-up. These gases must be vented so that they do not effect the electrical field or the wafer plating uniformity. Indeed, a separate upstream degasser removes most dissolved air from the main fluid flow path. The generated hydrogen gas, if not removed, becomes entrapped in the plating solution as bubbles or microbubbles and may interfere with the plating operation.
It therefore would be desirable to provide a means for venting hydrogen gas and any other trapped gases out of the plating solution before the solution reaches the wafer.